Measurements by spacecraft and ground-based observatories agree that the sun’s north and south magnetic poles are rapidly weakening. This could lead to a complete reversal of the sun’s global magnetic field before the end of the year.
From the National Solar Observatory (NSO):
The Sun is about to turn upside down – magnetically speaking, of course.
In recent months, we’ve seen an uptick in explosive solar events from dramatic X-class flares to Coronal Mass Ejections (CMEs), to powerful geomagnetic storms and a record-shattering sunspot count in June. The Sun may appear to be a raging inferno to the general public, but to solar scientists, it’s business as usual.
An active Sun was expected and these events are indications that the current Solar Cycle 25 is reaching its peak in activity, known as Solar Maximum. The Sun typically follows 11-year cycles bookended by periods of Maximum (high activity) and Minimum (low activity). When this cycle reaches Maximum, the Sun will begin to “quiet down” and decrease in activity as it transitions to Solar Minimum over the next decade. Once reached, Solar Cycle 26 will begin.
A simplified timeline depicting the polar magnetic field reversal in relation to solar cycles. The horizontal line represents the polar magnetic field’s polarity with red (+) and blue (-). Two Solar Cycles, N and N+1, show Maximum as the peak in their curve and Minimum as the lowest point. The polar field reversal does not mark the end of a solar cycle, but rather, the transition from Maximum to Minimum.
The Sun is busy, but one of the exciting developments is the reversal of its magnetic poles. Like Earth, the Sun has two magnetic poles, one positive and one negative. These poles change polarity, or magnetically flip, but unlike Earth’s poles that reverse roughly every 300,000 years, the solar poles flip about every 11 years!
The Sun’s polar field reversal is the major hallmark event that signals the end of a solar cycle’s Maximum period and ushers in the transition to Minimum. After the reversal, the newly established polar field will determine the strength of the next solar cycle. While the polar field reversal doesn’t happen in a dramatic display of firepower, it is an enormous global change with many consequences. For example, this is the only instance where activity like filament eruptions and CMEs – known to negatively impact Earth’s power and communication networks – can happen at any latitude on the Sun, including its poles.
The polar field reversal is closely related to sunspot activity. These images of sunspots were taken by the NSF’s Daniel K. Inoue Solar Telescope, showing a sunspot potentially at the end of its life cycle (left) and a group of sunspots interacting (right). Credit: NSF/AURA/NSO
The reversal happens when the Sun’s polar magnetic fields are weakened and replaced with a new field of the opposite polarity (e.g. going from positive to negative). The reversal is driven by sunspots, the magnetically-complex structures that create active regions where flares and other solar events originate. As sunspots emerge from the Sun’s interior in polar-opposite pairs, plasma flows rearrange their magnetic fields, stretching, weakening, and emphasizing the biases of their polarities. These weakened sunspot fields are carried by plasma flows towards the poles. The newly-arrived field tends to be of opposite magnetic polarity to the existing polar field, and when opposite polarities come into contact they destroy each other. This process comes to a head at the peak of the solar cycle, when enough opposite-polarity fields arrive at the poles, destroying the polar field, and replacing it with a new polar field of the opposite magnetic polarity.
A polar field reverse map using a top-down view of the Sun’s southern pole. Each figure represents an observing period: (a) January-February 2004 (b) January-February 2013 and (c) January 2017. Blue represents negative polarity and red as positive polarity. In 2004, the south pole’s magnetic field polarity was negative, surrounded by mostly positive magnetic flux. In 2013, the pole’s negative magnetic field was nearly gone. By 2017, the pole was rebuilt with a positive magnetic field. Credit: Pevtsov, A.A., Bertello, L., Nagovitsyn, Yu.A., Tlatov, A.G., Pipin, V.V.: 2021, “Long-term studies of photospheric magnetic fields on the Sun (A review article)“, J. Space Weather and Space Climate, 11, id. 4, 22pp, doi: 10.1051/swsc/2020069.
While polar field reversals vary in speed in timing, it generally takes a year or two to complete, but it varies. Solar Cycle 24’s north polar field took nearly five years to reverse!
On Earth, the effects of the polar field reversal are rarely felt, but the solar community is paying close attention. Orientation of magnetic fields in CMEs may be affected by large-scale magnetic fields. Thus, having negative (southern) polarity fields at the Sun’s North pole and positive (northern) polarity at the South pole would create magnetic topology opposite to Earth’s magnetic field. During that period, on average, the CMEs will have a slightly larger impact on Earth as compared with the period when the polar fields have opposite polarities. Thus, one should expect that after the polar magnetic field reversal and rebuilding, on average, the geomagnetic storms would be stronger than in the declining phase of Cycle 24 and the rising phase of Cycle 25.
The NSO operates the NSF’s six, ground-based solar telescopes that make up the GONG suite of ground-based solar telescopes. GONG stations are strategically located around the world to maintain a near round-the-clock surveillance of the visible Sun and have documented over 20 years of solar data. Observing the progress of the Sun’s polar migration is one of its many responsibilities.
The Sun’s polar fields are difficult to measure from Earth, given that the poles tilt towards us at only 7 degrees, at most. We can only see one pole at a time, but its magnetic field extends to about 30 degrees from each pole, bringing it into GONG’s view. GONG uses its ability to take continuous measurements of the Sun to study the progression of polar field reversals. This provides an important predictive capability – a stronger polar field could foreshadow a larger, more powerful solar cycle with more sunspots, flares, and other solar activity. Thus, providing us with an idea of what to expect during the next solar cycle.
Time-latitude plot (also known as a “butterfly diagram”) of the average radial magnetic field derived from NSO/GONG magnetograms (2006-present). The plot catches the final decline and minimum of cycle 23, all of cycle 24, and the beginning of cycle 25. The sunspots appear at higher latitudes at the beginning of each cycle than at the end, forming patterns like pairs of butterfly wings at low latitudes between +/- 30 degrees. The movement of decayed sunspot magnetic fields towards the poles shows up as oblique colored plumes between about +/- 30 and +/- 60 degrees latitude. The polar fields, the unipolar structures poleward of about +/- 60 degrees, respond to these plumes and change polarity shortly after the maximum of each cycle when the most field arrives. Updated from Petrie (2023), Solar Physics, Volume 298, Issue 3, article id.43
GONG uses direct observations of the magnetic fields to understand when the polar field is reversing. Another indication is the position of polar crown filaments (a “fibrous” structure consisting of plasma and magnetic field lines found in the Sun’s upper latitudes), which GONG has recently detected in the image below.
GONG captured a polar crown filament circled in white on August 2, 2023. The presence of these structures in high latitudes near the Sun’s poles is an indication of the polar field reversal. NSO scientists believe the reversal is getting close, potentially within less than a year from now. Credit: NSF/AURA/NSO
While the solar poles will “flip”, rest assured, there’s no need for us to flip out. This is a naturally occurring process on a massive scale that’s happened throughout the Sun’s lifetime. A polar field reversal would indicate a healthy solar cycle and that things will continue as it was in the past, whereas a lack of a reversal would indicate potential major changes to the solar cycle. As we anticipate the polar field reversal, we can expect to see a larger number of X-class flares, larger CMEs, and stronger geomagnetic storms – stay tuned for the next update!